1. Field of the Invention
The present invention relates to an apparatus for detecting the degree of throttle opening of an engine and which is capable of detecting the degree of opening of a throttle valve when an engine is idling ("the idling position").
2. Prior Art
It is known that an amount of fuel supplied, ignition timing, an amount of air bypassed and so on are controlled on the basis of a detection of the degree of opening of a throttle of an engine. For example, when an intake air sensor fails to function properly, an output of such a sensor is switched to a false signal calculated on the basic of a throttle opening signal corresponding to the degree of opening of a throttle valve, and a rotational frequency signal corresponding to the rotational frequency of an engine, and this false signal is used to calculate a necessary amount of fuel to be supplied by a well known calculating proceduce (cf. Japanese Patent Public Disclosure No. 13503/87).
By using a signal made with reference to an idling position (the zero position) of an engine as a throttle opening signal for controlling an amount of fuel supplied, ignition timing, an amount of air bypassed and so on, it may be possible to absorb the offset of a signal corresponding to the degree of opening of a throttle determined by the amount of intake air at the idling state, and to achieve optimum control with a high degree of accuracy.
A potentiometer is usually used for outputting an electrical signal corresponding to a throttle valve position as a detector which outputs a signal corresponding to an amount of throttle opening. Such a potentiometer operates to divide a voltage applied across the potentiometer and output a voltage corresponding to various positions from the idling position to the fully opened position. Conventionally, in order to accomplish optimum control with a high degree of accuracy, the position of such a detector is adjusted during a manufacturing process so that the detector may output a predetermined reference voltage. A throttle opening detector outputs the difference between an output signal of the detector and the predetermined reference voltage as a signal indicating an amount of throttle opening. On the basis of such amount of throttle opening, a control unit operates to control the amount of fuel suppliesd, ignition timing, the amount of air bypassed, and so on.
Since a conventional apparatus for detecting the amount of throttle opening of an engine is consituted as described above, the degree of control precision decreases in a case where positional deviation occurs during manufacture of a car, where a position at which a detector is mounted deviates due to prolonged usage of the detector, or where an idling position is changed in order to adjust the number of engine rotations when idling. For example, in the case of controlling an amount of fuel supplied, an output voltage of a detector at the throttle valve position during operation becomes lower than a normal value when the output voltage of the detector at an idling position becomes lower than a reference voltage. Accordingly, the amount of fuel supplied is reduced, the air/fuel ratio becomes lean and idling stability and the drivability deteriorates.